A power source unit is known in which a fuel cell or a battery and an electric component are housed in one casing or a plurality of casings coupled to each other. Japanese Patent Application Publication No. 2017-152286 describes an example of a power source device including a fuel cell as a power source. This document describes a fuel cell device that includes a lower casing housing the fuel cell, and an upper casing coupled onto the lower casing and housing electric components. Some of the electric components are attached to a back of a top plate of the upper casing.